IPv6 support

[netmilk]

Dredd is resolving hostnames always to the IPv4 address. When the backend is listening on IPv6 localhost ::1 and Dredd's server parameter is a hostname http://localhost:3000 the hostname is resolved to the IPv4 address 127.0.0.1 and all tests will fail with ECONNREFUSED:

error: Error connecting to server under test!

Some servers in some constellations are listening on the IPv6 only by default. The workaround solution is to force them to listen on the IPv4 localhost with some equivalent of:

rails server --binding=127.0.0.1

[philsturgeon]

🙌

[netmilk]

The reasoning why this is happening: https://groups.google.com/forum/#!topic/nodejs/0W6UqKy_klk

[netmilk]

I just realised this could be similar to this very old and closed issue: #126

[honzajavorek]

Could we do some kind of fallbacking and try/catching?

1. If Dredd gets a string localhost, it resolves it automatically to ::1 and tries to connect.
2. If ::1 fails to connect, Dredd tries 127.0.0.1.
3. If 127.0.0.1 fails to connect, then just pass localhost to the system and let it resolve ¯\_(ツ)_/¯

But that brings quite some overhead of reconnecting. This would have to happen just once, in the beginning, and then Dredd would need to respect the selected strategy for the rest of the requests.

Also, this could be an option:

1. If localhost is given to Dredd, let the system to resolve it.
2. If Dredd gets ECONNREFUSED, then try again with ::1 instead of localhost.

Again, Dredd would remember the selected strategy for all requests within the test run.